Process for the production of soy proteins having gel forming ability

ABSTRACT

A soy protein having excellent water-solubility, gel-forming ability, water-binding property and emulsifying property is obtained by separating the protein at a temperature below 80* C. in an acidic condition from soy milk which is obtained from soybean meal or soybeans by water extraction, alkalizing the protein with an alkalizing agent, returning the pH to about neutral with acid and thereafter heating the resulting protein solution at a temperature above 60* C.

Umted States Patent 1 1 3,607,860

1 Inventors YukiomiYamato 1511 1111.01 A23l 1 20 a s 50 Field 61Search... 99 17,14; Hitoshi Taniguchi, Osaka-shi; Sadao 2 0 1 12 123 5Nakayama, Osaka-fu; Teisaburo Tateishi, Osaka-tn, all of Japan [56]References Cited 1 1 gn 2 3 UNITED STATES PATENTS 22 Fi ed 0v.

E Patented Sept 21 1971 3,001,875 9 1961 s41: 99 17 [73] Assignee Fujion Company Limited Primary Examiner-A. Louis Monacell Osaka-shi, JapanAssistant Examiner-William Andrew Simons [32] Priority Dec.l,l966AtlorneyWoodhams, Blanchard and Flynn [33] Japan [54] PROCESS FOR THEPRODUCTION OF SOY PROTEINS HAVING GEL FORMING ABILITY 7 Claims, NoDrawings 52 1 US. Cl 260/1235, 99 17 ABSTRACT: A soy protein havingexcellent water-solubility, gel-forming ability, water-binding propertyand emulsifying property is obtained by separating the protein at atemperature below 80C. in an acidic condition from soy milk which isobtained from soybean meal or soybeans by water extraction, alkalizingthe protein with an alkalizing agent, returning the pH to about neutralwith acid and thereafter heating the resulting protein solution at atemperature above 60 C.

PROCESS FOR THE PRODUCTION OF SOY PROTEINS HAVING GEL FORMING ABILITYBACKGROUND OF THE INVENTION This invention relates to a process for theproduction of a water-soluble protein having excellent gel-formingability, water-binding ability and emulsifying property, which comprisesseparating the protein by acidifying soy milk which is obtained fromsoybean meal or soybeans by water extraction, alkalizing the protein,returning the pH to about neutral and thereafter heating the resultingprotein solution. Products excellent in gel strength andvisco-elasticity, and good in waterbinding ability and emulsifyingproperty can be obtained when the soy protein is utilized in meatprocessing and other fool processing.

DESCRIPTION OF THE PRIOR ART It has been conventional to make soyproteins by processing soybean meal directly, or by concentrating orisolating the proteins so that they can be utilized in food processing,such as in meat processing or unkneaded marine product processing.However, since the soy proteins are globular proteins, improvements inthe quality of the processed product are restricted spontaneously in theabove method because the soy proteins resist transformation of theirphysical state. The products of the above methods have many of thefollowing disadvantages: weakness in gel strength even though they mayhave some gel-forming ability; lack of gel strength and viscoelasticitywhich has detrimental effects on the extensibility and chewyness whenthe products are used to make kneaded marine products and hams orsausages; and inferiority in emulsifying property and water-bindingproperty. On the other hand, fibrous soy proteins which are obtained byspinning the soy proteins, making use of their coagulating properties,have been studied. However, only products which are not completelysatisfactory as a food have been obtained. These products are not onlylacking in smoothness but also inferior in water-binding and emulsifyingproperties. By using these methods, only products having insufficientemulsifying property, water-binding property, and especially gel-formingability are obtained. Particularly it was impossible to obtain a soyprotein product having such properties and a high watersolubility. It isearnestly desired to provide a soy protein which has a greatwater-binding property and a strong gel-forming ability, and which alsois capable of emulsifying fats which are added in great amounts inprocessed meat products.

SUMMARY OF THE INVENTION The animal proteins are fibrous and form netframeworks by intertwining with one another in processing. Since most ofthese proteins are soluble in saline solutions, they can form strongframeworks. Thereby it is considered that the soluble protein becomesinsoluble and affords strong gels by heating. The inventors have notedthe above facts and have discovered the present invention as a result ofinvestigations of the relationships of maintaining the solubility ofglobular soy proteins and fiber forming of protein molecules withchanges of pH as well as with heating.

Thus, the present invention comprises separating the protein at atemperature below 80 C. in an acidic condition from soy milk which isobtained from soybean meal or soybeans by water extraction, alkalizingsaid protein, returning the pH to about neutral, i.e., weakly alkaline,neutral or weakly acidic, and thereafter heating the resulting proteinsolution, whereby the emulsifying property, water-binding ability andgel-forming ability of said protein are increased with maintenance ofthe soluble state.

In the present invention, soy milk is first prepared by extractingprotein with water using soybean meal or soybeans as a startingmaterial. In order to obtain a final product having as high awater-solubility as possible, and to obtain a high yield in the waterextraction, it is preferable to employ soybean meal or soybeans having ahigh water-soluble protein content. It is necessary to carry out theextraction at a pH above six for the purpose of increasing theextraction effect. The extraction may be carried out at a lowtemperature or at a high temperature, such as at l00 C. When analkalizing agent or sulfite is added to increase the bleaching effectand the protein extraction effect, it is economical to employ a hightemperature. An alkalizing agent, such as sodium hydroxide, potassiumhydroxide, sodium carbonate or sodium bicarbonate is generally used; anda sulfite such as sodium sulfite or sodium bisulfite is generally used.

The soy milk is then acidified with an acid to precipitate and separatethe protein. In this case, the protein is separated in a curd state. Ingeneral, the pH of the protein separating step is suitably from 3.5 to5.0 and is preferably from 4.2 to 4.5. The acid used in acidifying thesoy milk is preferably an edible organic acid or an inorganic acid. Anorganic acid, such as acetic acid or lactic acid, or an inorganic acid,such as hydrochloric acid, phosphoric acid or sulfuric acid, is usuallyused. This operation is carried out at a temperature suitably below C.and preferably below 70 C. to recover the solubility of the protein bythe following operation. If the temperature is above 80 C., thewater-solubility of the protein is difficult to recover by thesubsequent treatment, and fibrous structure forming of the proteinmolecules is difficult to perform.

The precipitated and separated protein is then alkalized by analkalizing treatment. The alkalizing treatment is conducted by adding analkalizing agent. The alkalizing agent used in this case is as same asthat used in the above-water extraction step. In the alkalizing step,the pH is suitably from 9 to 12 and is, in particular, preferably from 9to II, If the pH is below 9, the visco-elasticity may becomeinsufficient, and if the pH is above 12, a browning reaction of theprotein may become prominent, the salt concentration of the finalproduct may be increased, and then the protein may be hydrolyzed,thereby decreasing its viscosity. The protein regains its water-solublestate and at the same time a fibrous structure forming of proteinmolecules may occur partially. As a result the protein obtains awater-binding property and a gel-forming ability. It is considered thatthe globular protein is converted to the fibrous protein by stirring andthe time elapsed, since a part of the soy protein is cleaved and theglobular protein is loosened in this case.

The protein is then approximately neutralized. Alkalinity is unfavorablein food, and it gives many unfavorable disadvantages in taste and onstorage, such as rapid putrefaction and bad color. Particularly in thepresent invention, the protein tends to become brown if it remains in analkaline condition during the subsequent heating step. Accordingly, itis necessary to neutralize the protein for the sake of the next step.The pH of the neutralizing step is suitably from 5 to 8 and preferablybetween 6 and 7. Thus, approximate neutralization refers to making theprotein weakly acid, neutral or weakly alkaline. The neutralization iscarried out by the use of an acid. In this case, the acid used isusually, an edible acid as described hereinbefore.

If the protein, separated by acidification from soy milk as describedabove, is immediately neutralized and dried and no alkalization step iscarried out, the protein may have an insufficient water-binding propertyand, at most, a hygroscopicity rate of I50 percent. In case the percenthydrated or hygroscopic product is heated to thermally denaturate andcoagulate the protein, a product with weak gel strength and inferiorvisco-elasticity may be obtained. Consequently, as described above, thesuccessive steps of acidification, alkalization (to pH9-l2) approximateneutralization including weak acidity and weak alkalinity, are extremelyimportant characteristics of the present invention. Furthermore, it isnecessary not to raise the temperature as much as possible during thesteps, each having a different pH after the isolation of the protein.

It seems economical that the protein may be extracted by the use of analkali from soybean meal or soybean meal leached in an aqueous acidsolution. In case a strong alkali is used during the extraction, theprotein molecules may be hydrolyzed and in that'event a decrease of theviscosity of the aqueous protein solution occurs. Therefore, thisextraction process has a fatal defect of remarkably decreasing theviscoelasticity in the heat coagulation of the protein. On the otherhand, according to the process of the present invention, the protein isnot hydrolized but becomes linear so that it is provided withvisco-clasticity, provided that the pH of the isolated protein isregulated between 9 and 12. Thus, in order to obtain the effects of thepresent invention, it is necessary that the protein, which is obtainedas an aqueous solution by the water extraction of soybean meal orsoybeans, is precipitated at its isoelectric point in order to increasethe concentration of the protein and then the pH is regulated between 9and 12. If other steps are employed in regulating the pH of the isolatedprotein, the effect in combination with the subsequent heating stepcannot be obtained.

In the present invention, the aqueous solution, of the protein,approximately neutralized as described hereinbefore, is then denaturatedby heating. It is necessary to conduct the heating at a temperatureabove 60 C., but immoderate heating, as described in detail hereinafter,should be prevented. The heating may be carried out either by blowingsteam directly on the protein solution, or by heating indirectly, for ashort period of time. The soy protein, which has become fibrous by thetreatment of changing the pH, is further assisted in this direction bythe heating step. The water-binding property which already existed maybe increased and at the same time the gel-forming ability may bestrengthened. Undoubtedly, it is necessary to maintain the previouslyobtained solubility. If heating is conducted at a temperature below 60C., a long time is required for obtaining the desired properties andconsequently the gel-forming ability may be decreased. However,immoderate heating should be avoided even when the temperature is above60 C. Heating can be carried out at a temperature in the range of from60 C. to 150 C., and it should be at a temperature at which the nitrogensolubility index (N.S.l.) of the resulting spray-dried protein powder,having a 10 percent water content, is above 40.

. g t Of Water soluble protein 100 Weight of the total protein Thesolubility is apt to be reduced, and the water-binding property and thegel-forming ability may be decreased by effecting immoderate heating. Ifthe protein liquor, produced by only adjusting the pH without conductingthe final thermal denaturation, is dried, a product having very weakgel-forming ability is obtained, and the effect according to the processof the present invention cannot be obtained. The effect of the presentinvention is achieved only in the case that a series of operations asdescribed above is accompanied by the heating step, and therefore saidheating step is extremely important in the present invention.

The effect of the present invention is shown in the following table:

Thermal denaturation after neutralization 4Fold test Thickness 3 mm.

Alkali treatment INSTRUCTIONS FOR 4-FOLD TEST 1. Mix homogeneously in acutter 200 gr. of said protein product 600 gr. of water 90 gr. of fat 15gr. ofcommon salt 2. Deforming 3. Stuffing into tube 4. Packing 5.Heating at 90 C. for 40 minutes 6. Cooling in tap water 7. Slicing intosheets of 3 mm. in thickness 8. The strips are then folded in half andthen are folded in half once more The results obtained by the 4-foldtest are shown in the table IDENTIFICATIONOF SYMBOLS Sheets which rentsare formed by folding in two Sheets in which rents are formed by foldingin four Sheets in which no rents are formed by folding in four Sheetswhich are of lower quality than B C Sheets which have little formingability D The water-binding property can be further improved accordingto the present invention. That is, the water-binding property, which inin the range between 200 percent and 220 percent before the heatingstep, is elevated to the range between 300 percent to 330 percent afterthe heating and drying treatment. At the same time, the gel-formingability can be improved. When an aqueous solution containing 13 percentby weight of the protein and 2.5 percent by weight of NaCl, is preparedand heated at C. for 30 minutes, gelation occurs. The gel is apt toeasily form rents if it is not heated, whereas if it is heated the gelmay have a strong self-supporting ability and visco-elasticity by whichrents are difficult to produce. Generally, the gel-forming ability maybe decreased when soy protein is mixed with fats in producing sausages.However, the protein according to the present invention exhibits aviscoelasticity from AA grade to A grade even though it may contain, forexample, from 10 percent to 15 percent of fats and 2.5 percent salt(NaCl). Ordinary soy proteins or proteins obtained without conducting thefinal heating process exhibit visco-elasticities merely from C grade toD grade. Furthermore, the emulsifying property is also promoted. Forexample, the emulsion formed by adding 5 percent of the protein producedby the process of the present invention to a mixture of water and fatsor oil at the weight ratio of l;l does not separate and can stillmaintain its consistency even when it is heated at a temperature abovel00 C.

In the present invention, the aqueous solution, of the soy protein,obtained by conducting thermal denaturation, can be dried, if required,by heating so that it can be preserved well and so that it will beconvenient to transport. Any methods generally used for this purpose areutilizable, but spray drying is preferable. An emulsion great instiffness is obtained when the soy protein so obtained is emulsifiedwith water and fats and oil or fatty meat. The protein is utilized as itis or as an emulsion in food processing and kneaded marine product andmeat processing, and in the production of ordinary sweets and foods.

The soy protein obtained according to the present invention is solublein water and has an excellent water-binding property, emulsifyingproperty and gel-forming ability. lt affords many excellentcharacteristic products having so-ealled viscoelasticity when it isemployed in food processing and kneaded marine and meat productprocessing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples arepresented further to illustrate the present invention. It is notintended, however, that the invention be limited to the details of theembodiments described therein.

Examplel One hundred k g. of water and, at the same time, 20 g. ofsodium sulfite were added to kg. of soybean meal having a nitrogensolubility index (N.S.T.) of 85 and soybeans having a N.S.l. of 92.Thereafter the extraction was conducted at ordinary temperature. 250-300ml. of concentrated hydrochloric acid was then added to the obtained soymilk, and the pH was adjusted to between 4.2 and 4.6. The precipitatedprotein thus obtained was separated by centrifuging and then wassuspending in water. The suspension was then neutralized with sodiumhydroxide, and the pH was adjusted to between 10 and 11 while it wasstirred vigorously to homogenize the liquor. After being thus alkalized,the alkaline liquor was again neutralized with hydrochloric acid to a pHbetween 6 and 7. The temperature of the neutralized liquor was raised to100 C. either by blowing with steam or by indirect heating andthereafter the liquor was dried by spray drying.

The qualities of the protein powder thus obtained were as follows:

Water content of the product Crude protein 86.3 percent N.S.T. 84.8

pH (in 1 percent aqueous solution) Ash 5.93 percent Gel-forming ability:The gel which was formed by molding a 2.5 percent common salt(NaCl)aqueous solution containing l2 percent by weight of the protein powderproduct prepared as described above, based on the entire weight of thesolution and heating the molded material at 80 C. for 30 minutes, had aself-supporting ability. A self-supporting gel was not formed when a soyprotein product produced by the conventional techniques was used in thesame way. The gel-forming ability is generally decreased when thesolution contains salt but, nevertheless, an excellent gelformingability can be obtained in accordance with the process of the presentinvention. An emulsion of great stiffness was obtained when 200 g. ofthe protein powder obtained as described above, 1 kg. of fatty pork, 50g. of common salt and 1 kg. of water were mixed and emulsified in acutter at a temperature of from 40 C. to 50 C. for about 10 minutes.This emulsion on heating at 1 10 C. for 30 minutes gave an emulsion ofhigh consistency which did not separate. ln the utilization of theemulsion of great stiffness as described above in meat processing,sausages rich in fat and stable in emulsifieation can be obtained.Example 2 Two hundred kg. of water and g. of sodium sulfite were addedto 10 kg. of soybean meal having a N.S.l. of 88 and the mixture washeated at 100 C. to extract soy milk from which the residue wasseparated. After cooling to 40 C., an acid was added to the soy milk,and the pH was adjusted to pH 4.5 to precipitate the protein. The sametreatments as described in example I were followed.

The qualities of the powdered soy protein thus obtained were as follows:

4.68 percent Water content of the product Crude protein 4.25 percent86.45 percent The gel-forming ability was excellent and was similar tothat of the product obtained in example 1.

Other pigments and spices were added to a mixture of 1 kg. of thepowdered soy protein obtained as described above, 3 kg. of water, 450 g.of lard and I0 g. of common salt. After being mixed and emulsifiedhomogeneously in a cutter, the mixture was cased and heated on a waterbath in such a manner that the central part was heated at C. for 30minutes. An oil-emulsified gel having elasticity and a homogeneous phasewas thus obtained, which could be used in producing sausage-like foods.

We claim:

1. In a process for producing a water-soluble soy protein whichcomprises the steps of obtaining soy mild from soybean meal or soybeansby water extraction at a pH above 6,

grecipitatin and separating the soy mild at a temperature elow 80 in anacidic condition to obtain protem and then treating the protein toimprove the gel-forming ability thereof, the improvement in saidtreating step which comprises adding an alkalizing agent to said proteinto adjust the pH of the protein to be in the range of) to l2, thenadding an acidifying agent to the protein to approximately neutralizethe protein, and thereafter heating the resultant approximately neutralprotein solution to a temperature in the range of from 60 C. to 150 C.to denature the protein whereby to obtain a watersoluble soy proteinhaving an improved gel-forming ability, as well as a water-bindingability and an emulsifying property.

2. A process according to claim I, wherein at least one compoundselected from the group consisting of alkalizing agents and sulfite'isadded in the step of extracting the soy milk with water.

3. A process according to claim 1, wherein the pH is adjusted to between4.2 and 4.5 in the precipitation and separation of said protein inacidic condition.

4. A process according to claim 1, wherein the pH is adjusted to between9 and l l in the adjustment of the pH of said protein with an alkalizingagent.

5. A process according to claim 1, wherein the heating step is conductedat a temperature in the range of from 80 C. to C.

6. A process according to claim 1 in which, after the heating step, theprotein solution is spray dried.

7. A process according to claim 1 in which, in the treating step, theprotein is suspended in water, then the alkalizing agent is addedthereto to adjust the pH of the suspension to be in the range of 10 toI] while stirring the suspension to homogenize same and then adding theacidifying agent to adjust the pH to be in the range off; to 7.

2. A process according to claim 1, wherein at least one compoundselected from the group consisting of alkalizing agents and sulfite isadded in the step of extracting the soy milk with water.
 3. A processaccording to claim 1, wherein the pH is adjusted to between 4.2 and 4.5in the precipitation and separation of said protein in acidic condition.4. A process according to claim 1, wherein the pH is adjusted to between9 and 11 in the adjustment of the pH of said protein with an alkalizingagent.
 5. A process according to claim 1, wherein the heating step isconducted at a temperature in the range of from 80* C. to 120* C.
 6. Aprocess according to claim 1 in which, after the heating step, theprotein solution is spray dried.
 7. A process according to claim 1 inwhich, in the treating step, the protein is suspended in water, then thealkalizing agent is added thereto to adjust the pH of the suspension tobe in the range of 10 to 11 while stirring the suspension to homogenizesame and then adding the acidifying agent to adjust the pH to be in therange of 6 to 7.